Heat extractor for magnetic reader-writer

ABSTRACT

The Increased power needed to drive the write coil in a contemporary read-write magnetic head leads to greater thermal pole tip protrusion during writer activation. This problem has been overcome by including a heat diffuser on top of the return portion of the upper coils together with a thermally conductive pedestal that connects it to the substrate. During writer activation, the joule heating generated by the write current at the coils is extracted through the heat diffuser and subsequently dissipated in the substrate. The resulting lower temperature rise in the pole tip area leads to lower thermal protrusion.

FIELD OF THE INVENTION

The invention relates to the general field of magnetic read-write headswith particular reference to dissipating heat generated by the writecoil.

BACKGROUND OF THE INVENTION

FIG. 1 shows a cross-sectional view of a read-write head of the priorart. Seen there are substrate 10 on which is undercoat 11. Magnetic readunit 13 is seen sandwiched between reader shields 12. The read unit is amagneto-resistive type such as a GMR (giant magneto-resistance) or MTJ(magnetic tunnel junction).

Directly above the upper of the two shields 12 is horizontal portion 14of the bottom pole from which vertical portion 15 extends, its outeredge being part of the ABS (air bearing surface). Some distance awayfrom vertical bottom pole 15 is yoke 16 that also extends upwards fromthe horizontal bottom pole, but to a slightly greater height than thevertical lower pole. Non-magnetic write gap layer 20 lies on verticalpole 15 and extends from the ABS to the edge of yoke 16.

Surrounding yoke 16 is coil(s) 17, the number of coils being a designchoice which will be discussed in greater detail below. Hard-bakedphotoresist 18 is used to encapsulate the coil(s) as well as the yoke.The writer magnetic circuit is completed through top pole 21 which is inmagnetic contact with yoke 16 and is separated from vertical pole 15 bywrite gap layer 20. The structure of FIG. 1 is completed by fillerinsulation 19 and by overcoat layer 22.

As areal density requirements have become more stringent for magneticrecording read/write heads, the complexity of the writer structuredesign has grown significantly. The need for a higher number of coilturns in the writer for stronger overwrite magnetic field, whileminimizing the coil DC resistance, result in a trend to multi-layer coilwriter structures. The frequency extendability requirement for higherdata rate applications dictates the need for a shorter yoke length andthe associated lower inductance, which also necessitates a multi-coillayer writer structure. While this achieves the required magneticperformance, the multi-layer coil writer has an intrinsicdeficiency—poor heat dissipation for the upper (top) layer coils. Higherthermal pole tip protrusion during writer activation resulting from thisdrawback creates reliability problems relative to single-layer coilwriter designs.

A routine search of the prior art was performed with the followingreferences of interest being found:

In U.S. Pat. No. 6,181,514, Santini et al. disclose a nonorganicinsulating material on the coil as a heat dissipater. In U.S. Pat. No.6,466,404, Crue, Jr. et al. show AlN or other material as an undercoatunder the coil to dissipate heat and, in U.S. Pat. No. 6,381,094, Gillteaches using gold and tantalum as a heat sink layer.

SUMMARY OF THE INVENTION

It has been an object of at least one embodiment of the presentinvention to provide a magnetic read-write head that exhibits little orno protrusion, due to thermal expansion, of the vertical write poleduring operation of the device.

Another object of at least one embodiment of the present invention hasbeen to achieve said reduced thermal pole protrusion through theprovision of improved cooling of the write coils.

Still another object of at least one embodiment of the present inventionhas been to provide a process for the manufacture of said improved readwrite-head.

These objects have been achieved by including a heat diffuser on top ofthe return portion of the upper coils together with a pedestal thatconnects it to the substrate. During writer activation, the jouleheating generated by the write current at the coils is extracted throughthe heat diffuser and subsequently dissipated in the substrate. Theresulting lower temperature rise in the pole tip area leads to lowerthermal strain/stress and induced protrusion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a typical prior art planar read-write magnetic head.

FIG. 2 FIG. 2 shows the starting point for the process of the presentinvention.

FIGS. 3 and 4 show intermediate steps in the process of the presentinvention.

FIG. 5 shows the final structure that results from a first embodiment ofthe process of the present invention.

FIGS. 6 and 7 show steps in a second embodiment of the process of thepresent invention.

FIGS. 8 and 9 show the results of a simulation of the performance of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

We now disclose a structure having a heat extractor to dissipate thecoil heat generation through an alternative path inside the slider forimproved current driven thermal pole tip protrusion. The preferredembodiment uses a combination of heat diffuser and pedestal for heatsinking to the slider substrate. This heat extractor extracts anddissipates the heat generated during writer activation in multiple coillayer writer structures to reduce the thermal pole tip protrusion.

To remedy the undesirable problem of higher thermal pole tip protrusion,a novel heat extractor structure has been designed to enhance the heatdissipation of the top layer coils to the slider substrate. Thisinvented heat extractor structure is applicable to other multi-layercoil writer structures such as nine-turn double planar writer with 12micron yoke length, stitched-pole writer, perpendicular writer, etc.This heat extractor is also compatible with various reader shieldstructures. In fact, for smaller shield sizes, the conductive pedestal(see below) can be made larger for even better heat sinking effect.

The heat extractor consists of a heat diffuser on top of the returnportion of the upper coils and a pedestal connecting the diffuser to theundercoat. During writer activation, the joule heating generated by thewrite current at the coils can be extracted through the heat diffuserand subsequently dissipated onto the substrate through the pedestal.This alternative heat sink path alleviates the “heat dwelling” problemof the existing two layer coil writer at the interface of the upper andlower coils, thus reducing the temperature rise in the coil and devicearea. Lower temperature rise in the pole tip area leads to lower thermalstrain/stress and induced protrusion.

The material for the heat diffuser and pedestal is constrained to benon-magnetic and should have high thermal conductivity. Copper is a goodcandidate due to its superior thermal conductivity and its easiness forplating process integration, but other materials such as tungsten andmolybdenum (which have lower coefficients of thermal expansion) as wellas silicon, ruthenium, rhodium, iridium, and their mutual alloys, couldbe substituted. Since the extractor structure is encapsulated within theslider body, material corrosion during backend processing is not aconcern. Also, the extractor is further recessed away from the ABSsurface so the isothermal protrusion associated with volumetricexpansion of materials with higher coefficient of thermal expansion(CTE) is lessened. Therefore, the material selection possibilities forhigher CTE materials are increased.

The heat diffuser and pedestal should be as wide as space permits(typically between about 1 and 2.5 microns thick and between about 100and 125 microns wide for the extractor layer and a cross-sectional areaof at least 10,000 sq. microns for the pedestal) for improved heatdissipation, following the principle of larger surface area to volumeratio in thermal design. The diffuser should cover the area of thehard-baked photo resist for more effective cooling since the thermalconductivity of photo resist is extremely poor. The insulator separatingthe yoke diffuser and coil-diffuser is also preferred to be thin (inrange of between about 2,000 and 8,000 Angstroms).

Referring now to FIG. 2, the process to manufacture the invention beginswith substrate 10 onto which is deposited undercoat 11. Magnetic readhead 13, sandwiched between upper and lower magnetic shield layers 12,is then formed on said undercoat. With read head assembly 13 in place,bottom horizontal magnetic pole 14 is formed on upper magnetic shield12, following which thermally conductive pedestal 23 (that does notcontact bottom horizontal magnetic pole 14) is formed on undercoat 11,giving the structure the appearance shown in FIG. 2.

Next, as seen in FIG. 3, layer of insulation 19 is deposited on allexposed surfaces followed by planarization down to the level of bottomhorizontal magnetic pole 14. Then, vertical bottom magnetic pole 15 isformed, its front surface being part of the ABS, along with magneticyoke 16 that extends upwards from the bottom horizontal pole to aslightly greater height than vertical bottom pole.

Write coil 17 (which may have one or more turns) is then formed. Itsurrounds yoke 16 and rests on bottom horizontal magnetic pole 14,though it is insulated therefrom. This is followed by the deposition ofphotoresist 18, in an amount that is sufficient to fully cover, andthereby electrically insulate, write coil 17. Photoresist 18 is nowpatterned so that it covers all exposed surfaces except for pedestal 23and this photoresist is then hard baked. An insulating layer is thendeposited onto the patterned write coil and photoresist, covering allexposed surfaces except pedestal 23 and magnetic yoke 16.

Moving next to FIG. 4, layer of non-magnetic material 20, that extendsfrom over bottom vertical pole 15 as far as the outer edge of yoke 16,is then deposited and patterned so as to form write gap 20. Top magneticpole 21 is then formed, extending from the ABS as far as, and makingmagnetic contact with, yoke 16. Then, in a key feature of the invention,layer of thermally conductive material 41 is deposited on all exposedsurfaces.

Finally, as can be seen in FIG. 5, the structure is then planarizeduntil top magnetic pole 21 is just exposed, thereby forming heatdiffuser 41 that, together with thermally conductive pedestal 23,provides a thermal path between the write coil(s) and theundercoat/substrate. The presence of this thermal path serves to reduce,or eliminate, protrusion, due to thermal expansion, of the verticalwrite pole during operation of the device.

Formation of the device concludes with the deposition of overcoat layer22 onto all exposed surfaces.

A second embodiment of the invention is manufactured in a similar mannerto that detailed above to the point where the structure is as seen inFIG. 2, but without the formation of pedestal 23. Instead, asillustrated in FIG. 6, first layer of insulation 19 is deposited ontoall exposed surfaces and then planarized down to the level of bottomhorizontal magnetic pole 14.

Then, vertical bottom magnetic pole 15 is formed, as before, along withmagnetic yoke 16 followed by the formation of write coil(s) 17 thatsurrounds yoke 16. Next, photoresist 18, sufficient to fully cover thecoils, is deposited thereby electrically insulating them. Photoresist 18is now patterned so as to leave uncovered that portion of firstinsulation layer 19 that overlies only the substrate.

After the photoresist has been hard baked, layer of non-magneticmaterial 20, that extends from over the vertical bottom pole as far asthe yoke, is deposited to form the write gap. Second layer of insulatingmaterial 61 is then deposited and planarized until write gap layer 20 isjust exposed and via hole 62, that extends as far as the undercoat, isformed.

Moving on to FIG. 7, via hole 73 is overfilled with thermally conductivematerial and the structure is planarized until top magnetic pole 21 isjust exposed. As in the first embodiment, the completed structurefeatures heat diffuser 41 that, together with the filled via hole,provides a thermal path between the write coil(s) and the undercoat,whereby pole protrusion due to thermal expansion is reduced. The processconcludes with the deposition of overcoat 22 onto all exposed surfaces,giving the completed structure the appearance illustrated in FIG. 7.

Confirmation of the Effectiveness of the Invention

To verify the ability of this heat extractor structure to reduce thermalpole tip protrusion during writer activation, a finite-element model(FEM) was created for simulation under steady-state conditions for theplanar writer shown in FIGS. 5 and 7. The material selected for diffuserand pedestal in the simulation was copper. The layout in the simulationof the diffuser was 43 μm depth by 66 μm width and, for the pedestal, 42μm depth by 100 μm width. The distance between the back of the yoke andthe front of diffuser in the model was 3 μm. The spacing between the topcoil surface and the bottom of the diffuser was 0.2 and 0.6 μmrespectively.

The simulation results for PTP (pole tip protrusion), based on 40 mA DCwriter current and 2.91 ohm coil DCR (direct current resistance) in thedisk-flying and non-flying conditions are tabulated in TABLE I below:TABLE I Non-flying Flying Configuration PTP Improvement PTP ImprovementPrior art device 2.42 nm — 1.55 nm — 0.6 μm extractor 2.04 nm 16% 1.33nm 14% spacing 0.2 μm extractor 1.88 nm 22% 1.27 nm 19% spacing

The protrusion calculation is referenced at the entire slider's leadingedge. The above result indicates that the heat extractor improves themaximum protrusion during writer activation ranging from 16% to 22%under non-flying condition and 14% to 19% under disk flying conditions.An example of the protrusion profile comparison under non-flyingcondition among the 3 simulated configurations is shown in FIG. 8. Curve81 is for the 0.6 micron extractor, curve 82 is for the 0.2 micronextractor, and curve 83 is for the prior art device. The effectivenesscan be further improved with larger areas for diffuser and pedestalcompared to the exemplary configurations used in the simulation.

The added heat extractor structure was also verified with FEM simulationto evaluate its isothermal protrusion performance. The simulationresults based on 40° C. ambient temperature rise are shown in FIG. 9.

The isothermal protrusion profiles for slider with and without the heatextractor are almost identical (<1% difference). This shows that theaddition of heat extractor structure does not degrade the isothermalprotrusion performance. The result distinguishes this heat extractordesign from other heat sink/diffuser proposals that exhibit significantisothermal protrusion increase due to the location being too close oreven exposed to the ABS surface.

We conclude by noting that the simulation results reported above do notnecessarily represent the best possible improvements obtainable with theinvention. For example, heat dissipation could be further improved bysubstituting aluminum nitride as the insulation in place of the aluminumoxide that is normally used.

1. A method to dissipate heat generated from a source within amicro-structure, that is on a substrate, comprising: forming a thermallyconductive pedestal that extends upwards from said substrate; andforming a layer of thermally conductive material that contacts saidpedestal and extends therefrom as far as said heat source.
 2. The methodof claim 1 wherein said layer of thermally conductive material and saidconductive pedestal have a thermal conductivity between about 100 and400 W/m.K.
 3. The method of claim 1 wherein said layer of thermallyconductive material is selected from the group consisting of copper,tungsten, molybdenum, silicon, ruthenium, rhodium, iridium, and theirmutual alloys.
 4. The method of claim 1 wherein said layer of thermallyconductive material has a thickness between about 1 and 2.5 microns. 5.The method of claim 1 wherein said pedestal has a cross-sectional areathat is between about 10,000 and 15,000 sq. microns.
 6. The method ofclaim 1 wherein said source generates heat at a rate between about 4 and15 milliwatts.
 7. A process to manufacture a magnetic write head, havingan ABS, comprising: providing a substrate and depositing thereon anundercoat; forming a magnetic read head, sandwiched between upper andlower magnetic shield layers, on said undercoat; on said upper magneticshield, forming a bottom horizontal magnetic pole; forming on saidundercoat a thermally conductive pedestal that does not contact saidbottom horizontal magnetic pole; depositing a layer of insulation on allexposed surfaces and then planarizing down to the level of said bottomhorizontal magnetic pole; forming a vertical bottom magnetic pole,having a front surface that is part of the ABS, and a magnetic yoke thatextends upwards from said bottom horizontal pole to a height thatexceeds that of said vertical bottom pole; forming, on said bottomhorizontal magnetic pole, a write coil that surrounds said yoke;depositing photoresist, sufficient to fully cover, and therebyelectrically insulate, said write coil; patterning said photoresist soas to leave only said pedestal uncovered; hard baking the photoresist;forming a layer of non-magnetic material that extends from over thevertical bottom pole as far as said yoke, thereby forming a write gap;forming, on said layer of non-magnetic material and on said yoke, a topmagnetic pole; depositing a layer of thermally conductive material onall exposed surfaces and then planarizing until said top magnetic poleis just exposed, thereby forming a heat diffuser that, together withsaid thermally conductive pedestal, provides a thermal path between saidwrite coil and said undercoat, whereby pole protrusion due to thermalexpansion is reduced; and then depositing an overcoat onto all exposedsurfaces.
 8. The process recited in claim 7 wherein said write coilcomprises two or more turns.
 9. The process recited in claim 7 whereinsaid pedestal has a height of between about 100 and 125 microns.
 10. Theprocess recited in claim 7 wherein said layer of thermally conductingmaterial is formed to have a width between about 100 and 125 microns.11. The process recited in claim 7 wherein said layer of thermallyconductive material and said conductive pedestal have a thermalconductivity between about 100 and 400 W/m.K.
 12. The process recited inclaim 7 wherein said layer of thermally conductive material is selectedfrom the group consisting of copper, tungsten, molybdenum, silicon,ruthenium, rhodium, iridium, and their mutual alloys.
 13. The processrecited in claim 7 wherein said layer of thermally conductive materialhas a thickness between about 1 and 2.5 microns.
 14. The process recitedin claim 7 wherein said pedestal has a cross-sectional area that isbetween about 10,000 and 15,000 sq. microns.
 15. The process recited inclaim 7 wherein said write coil generates heat at a rate between about 4and 15 milliwatts.
 16. A process to manufacture a magnetic write head,having an ABS, comprising: providing a substrate and depositing thereonan undercoat; forming a magnetic read head, sandwiched between upper andlower magnetic shield layers, on said undercoat; on said upper magneticshield, forming a bottom horizontal magnetic pole; depositing a firstlayer of insulation on all exposed surfaces and then planarizing down tothe level of said bottom horizontal magnetic pole; forming a verticalbottom magnetic pole, having a front surface that is part of the ABS,and a magnetic yoke that extends upwards from said bottom horizontalpole to a height that exceeds that of said vertical bottom pole;forming, on said bottom horizontal magnetic pole, a write coil thatsurrounds said yoke; depositing photoresist, sufficient to fully cover,and thereby electrically insulate, said write coil; patterning saidphotoresist so as to leave uncovered a portion of said first layer ofinsulation that overlies only said substrate; hard baking thephotoresist; forming a layer of non-magnetic material that extends fromover the vertical bottom pole as far as said yoke, thereby forming awrite gap layer; depositing a second layer of insulating material andthen planarizing until said write gap layer is just exposed; forming,through said first and second insulating layers, a via hole that extendsas far as said undercoat; forming, on said write gap layer and on saidyoke, a top magnetic pole; depositing a layer of thermally conductivematerial on all exposed surfaces, sufficient to over-fill said via hole;then planarizing until said top magnetic pole is just exposed, therebyforming a heat diffuser that, together with said filled via hole,provides a thermal path between said write coil and said undercoat,whereby pole protrusion due to thermal expansion is reduced; and thendepositing an overcoat onto all exposed surfaces.
 17. The processrecited in claim 16 wherein said write coil comprises two or more turns.18. The process recited in claim 16 wherein said via hole is formed to adepth of between about 100 and 125 microns.
 19. The process recited inclaim 16 wherein said layer of thermally conducting material is formedto have a width between about 100 and 125 microns.
 20. The processrecited in claim 16 wherein said layer of thermally conductive materialhas a thermal conductivity between about 100 and 400 W/m.K.
 21. Theprocess recited in claim 16 wherein said layer of thermally conductivematerial is selected from the group consisting of copper, tungsten,molybdenum, silicon, ruthenium, rhodium, iridium, and their mutualalloys.
 22. The process recited in claim 16 wherein said layer ofthermally conductive material has a thickness between about 1 and 2.5microns.
 23. The process recited in claim 16 wherein said via hole has across-sectional area that is between about 10,000 and 15,000 sq.microns.
 24. The process recited in claim 16 wherein said write coilgenerates heat at a rate between about 4 and 15 milliwatts.
 25. A heatextractor for a micro-structure that includes a heat source and asubstrate, comprising: a thermally conductive pedestal that extendsupwards from said substrate; and a layer of thermally conductivematerial that contacts said pedestal and extends therefrom as far assaid heat source.
 26. The heat extractor described in claim 25 whereinsaid layer of thermally conductive material and said conductive pedestalhave a thermal conductivity between about 100 and 400 W/m.K.
 27. Theheat extractor described in claim 25 wherein said layer of thermallyconductive material is selected from the group consisting of copper,tungsten, molybdenum, silicon, ruthenium, rhodium, iridium, and theirmutual alloys.
 28. The heat extractor described in claim 25 wherein saidlayer of thermally conductive material has a thickness between about 1and 2.5 microns.
 29. The heat extractor described in claim 25 whereinsaid pedestal has a cross-sectional area that is between about 10,000and 15,00 sq. microns.
 30. A magnetic read-write head, having an ABS,comprising: a substrate on which is an undercoat; a magnetic read head,sandwiched between upper and lower magnetic shield layers, on saidundercoat; on said upper magnetic shield, a bottom horizontal magneticpole; on said undercoat a thermally conductive pedestal that does notcontact said bottom horizontal magnetic pole; a layer of insulationextending from said undercoat as far as the level of said bottomhorizontal magnetic pole; a vertical bottom magnetic pole, having afront surface that is part of the ABS, and a magnetic yoke that extendsupwards from said bottom horizontal pole to a height that exceeds thatof said vertical bottom pole; on said bottom horizontal magnetic pole, awrite coil that surrounds said yoke; a layer of hard baked photoresist,fully covering said write coil and not present over said pedestal; awrite gap layer of non-magnetic material that extends from over thevertical bottom pole as far as said yoke; on said layer of non-magneticmaterial and on said yoke, a top magnetic pole; a layer of thermallyconductive material that contacts said pedestal and extends therefrom asfar as over said write coil, whereby there is reduced pole protrusiondue to thermal expansion; and an overcoat layer on said top magneticpole and on said layer of thermally conductive material.
 31. Theread-write head described in claim 30 wherein said write coil has two ormore turns.
 32. The read-write head described in claim 30 wherein saidpedestal has a height of between about 100 and 125 microns.
 33. Theread-write head described in claim 30 wherein said layer of thermallyconducting material has a width between about 100 and 125 microns. 34.The read-write head described in claim 30 wherein said layer ofthermally conductive material has a thermal conductivity between about100 and 400 W/m.K.
 35. The read-write head described in claim 30 whereinsaid layer of thermally conductive material is selected from the groupconsisting of copper, tungsten, molybdenum, silicon, ruthenium, rhodium,iridium, and their mutual alloys.
 36. The read-write head described inclaim 30 wherein said layer of thermally conductive material has athickness between about 1 and 2.5 microns.
 37. The read-write headdescribed in claim 30 wherein said pedestal has a cross-sectional areathat is between about 10,000 and 15,000 sq. microns.
 38. The read-writehead described in claim 30 wherein said write coil generates heat at arate between about 4 and 15 milliwatts.
 39. The read-write headdescribed in claim 30 wherein pole protrusion due to thermal expansionis less than about 10 Angstroms.